Continuously variable transmission

ABSTRACT

A continuously variable transmission includes a first asymmetrical differential, having a transmission input shaft and a first output shaft, aligned along a transmission axis, a second asymmetrical differential, having a transmission output shaft and a first input shaft, aligned along the transmission axis, and a reduction gear unit, coupled between the first output shaft of the first asymmetrical differential and the first input shaft of the second asymmetrical differential. Rotation of the input shaft at a first input speed and torque is converted into rotation of the transmission output shaft at a second output speed and torque that varies independently of the first input speed and torque in response to a rotational resistance on the transmission output shaft.

PRIORITY CLAIM

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/094,645, filed on Dec. 19, 2014, and entitledCONTINUOUSLY VARIABLE TRANSMISSION, the disclosure of which isincorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present application relates to mechanical transmissions. Moreparticularly, the present disclosure provides a continuously variabletransmission that passively senses and automatically adjusts to changesin loads, and provides the high torque advantages of mechanical gears.

BACKGROUND

Machines that are powered by an engine, such as motor vehicles,typically include a transmission to adjust the rotational speed andtorque between the engine and the machine. Some engines, such asinternal combustion engines, typically operate at higher rotationalspeeds (except when operating in an overdrive condition, for example)than are desired as output for their associated machine. On the otherhand, some engines, such as electric motors, may typically operate atlower rotational speeds than are desired for their associated machine.However, various types of engines will have characteristic operatingrange(s) that is/are considered most desirable in terms of operationalspeed, torque, power output, and for the mechanical health and longevityof the engine. Accordingly, a mechanical transmission is typicallyprovided between an engine and its associated machine so that a driveratio between the engine output and the machine output can be variedover a desired operating range of the engine. Such transmissionstypically include a power train of multiple gears of varying diametersand gear ratios that can be shifted between different gear combinations,to provide a desired output rotational speed for the machine that variesfrom the engine operating speed, in various power and torque conditions.This allows the machine be operated closer to its desired operatingtorque and speed range while permitting the output to vary overdifferent and usually broader torque and speed ranges.

In automobiles, for example, manual transmissions were developed toallow a user to manually select one of several discrete gear ratios.Automatic transmissions were later developed in which an appropriategear ratio for given conditions and power demand are automaticallydetermined and implemented. Conventional transmissions, whether manualor automatic, are often complicated, heavy, and bulky, and thereforeexpensive. Further, such systems often shift abruptly in a steppedmanner between discrete ratios, rather than in a smooth and continuousmanner. These characteristics of conventional transmissions tend toreduce the overall efficiency of the machine, and also introduceoperational characteristics that are considered undesirable.

These characteristics become particularly noticeable in othertransmission applications. For example, farm equipment typicallyoperates within a relatively narrow range of speeds. However, a tractor,for example, may have another piece of farm equipment connected to apower take-off (PTO). The additional piece of farm equipment may bepreferably operated at a nearly constant operational speed, thusinvolving a relatively large number of gear ratios to drive the tractorat varying speeds while maintaining the engine at a nearly constantrotational speed for the sake of the PTO.

To address some of these issues related to mechanical transmissions,continuously variable transmissions have been developed. Continuouslyvariable transmissions select and provide output power along acontinuously variable range of gear ratios, rather than in discretesteps, thus allowing more optimum and continuous operation of theengine. However, conventional continuously variable transmissionstypically employ belt and pulley systems or frictional cones and thelike, which rely upon friction for operation. They can also berelatively mechanically complicated. Consequently, known continuouslyvariable transmissions tend to present significant mechanical losses,which reduces their efficiency, and are also limited in the maximumtorque which they can transfer, thus limiting their use to relativelylow torque applications (e.g. small motor vehicles). Other concerns alsoexist with conventional manual, automatic and continuously variabletransmissions.

The present application is directed to overcoming one or more of theabove-mentioned issues.

SUMMARY

It has been recognized that it would be desirable to have a continuouslyvariable transmission that has relatively low mechanical losses.

It has also been recognized that it would be desirable to have acontinuously variable transmission that can be scaled up to high torqueapplications.

It has also been recognized that it would be desirable to have acontinuously variable transmission that is relatively mechanicallysimple.

In accordance with one aspect thereof, the present disclosure provides acontinuously variable transmission, including a first asymmetricaldifferential, having a transmission input shaft and a first outputshaft, aligned along a transmission axis, a second asymmetricaldifferential, having a transmission output shaft and a first inputshaft, aligned along the transmission axis, and a reduction gear unit,coupled between the first output shaft of the first asymmetricaldifferential and the first input shaft of the second asymmetricaldifferential. Rotation of the input shaft at a first input speed andtorque is converted into rotation of the transmission output shaft at asecond output speed and torque that varies independently of the firstinput speed and torque in response to a rotational resistance on thetransmission output shaft.

In accordance with another aspect thereof, the present disclosureprovides a continuously variable transmission, including a firstasymmetrical differential, a second asymmetrical differential, and areduction gear unit, having a gear ratio, disposed between the first andsecond asymmetrical differentials. The first asymmetrical differentialhas an input shaft configured for connection to an output shaft of amotor, and a coaxial pair of first output shafts, including an outeroutput shaft and an inner output shaft. The input shaft and the outputshafts are disposed along a common transmission axis. The secondasymmetrical differential has an output shaft, and a coaxial pair ofinput shafts, including an outer input shaft and an inner input shaft.The output shaft and the input shafts being disposed along thetransmission axis, and the inner input shaft is an extension of theinner output shaft. The reduction gear unit has a reduction gear inputcoupled to the outer output shaft, and a reduction gear output coupledto the outer input shaft, whereby rotation of the input shaft of thefirst asymmetrical differential at a first input speed and torque isconverted into rotation of the output shaft at a second output speed andtorque that varies independently of the first input speed and torque indirect response to rotational resistance on the output shaft.

In accordance with yet another aspect thereof, the present disclosureprovides a continuously variable drive system, including a motor, havinga drive shaft, and a transmission output shaft, disposed along atransmission axis. A first asymmetrical differential has an input shaftcoupled to the drive shaft, and first and second coaxial output shafts,disposed along the transmission axis. A reduction gear has an inputcoupled to the first output shaft of the first asymmetricaldifferential, and an output. A second asymmetrical differential has afirst input shaft coupled to the output of the reduction gear, and asecond input shaft coupled to the second output shaft of the firstasymmetrical differential, disposed along the transmission axis. A speedand torque of the transmission output shaft varies independently of aspeed and torque of the drive shaft in direct response to rotationalresistance on the transmission output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of one embodiment of a continuously variabletransmission in accordance with the present disclosure.

FIG. 2 is perspective view of the continuously variable transmission ofFIG. 1.

FIG. 3 is an exploded perspective view showing the components parts ofthe continuously variable transmission of FIG. 1.

FIG. 4 is a side, cross-sectional view of the continuously variabletransmission of FIG. 1.

FIG. 5A is a perspective view of an asymmetrical differential.

FIG. 5B is an exploded perspective view of the asymmetrical differentialof FIG. 5A.

FIG. 6A is a side view of a conventional limited slip differential.

FIG. 6B is a cross-sectional view of the conventional differential ofFIG. 6A.

FIG. 7A is a side view of an asymmetrical differential as disclosedherein.

FIG. 7B is a cross-sectional view of the asymmetrical differential ofFIG. 7A.

FIG. 8 is a side view of the continuously variable transmission of FIG.1, partially disassembled to show the high speed/low torque shaft andits bevel gears.

FIG. 9 is a perspective view of the continuously variable transmissionof FIG. 1, partially disassembled to show the reduction gear unit.

FIG. 10 is close-up perspective view of the reduction gear unit and aportion of the bevel gear sets of the continuously variable transmissionof FIG. 1.

FIG. 11 is a partially disassembled perspective view of an embodiment ofa reduction gear unit configured for use with the transmission of FIG.1, having a 3-gear planetary gear arrangement.

FIG. 12 is an exploded perspective view of an embodiment of a reductiongear unit configured for use with the transmission of FIG. 1, having a2-gear planetary gear arrangement.

FIG. 13 is a partial schematic side view of the continuously variabletransmission of FIG. 1, showing an embodiment of an electronic controlsystem.

FIG. 14 is a perspective view of another embodiment of a continuouslyvariable transmission in accordance with the present disclosure, havinga selective speed and torque adjustment mechanism.

FIG. 15 is an exploded perspective view of the selective speed andtorque adjustment mechanism configured for use in with the continuouslyvariable transmission of FIG. 14.

FIG. 16 is a perspective view of another embodiment of a continuouslyvariable transmission in accordance with the present disclosure, havinga selective speed and torque adjustment mechanism.

FIG. 17 is an exploded perspective view of the selective speed andtorque adjustment mechanism configured for use in with the continuouslyvariable transmission of FIG. 13.

FIG. 18 is a partial schematic perspective view of a continuouslyvariable transmission like that of FIG. 13, showing an embodiment of anelectronic control system.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. However,it should be understood that the disclosure is not intended to belimited to the particular forms disclosed. Rather, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

As noted above, continuously variable transmissions that are currentlyknown generally include belts and pulleys, frictionally engaged cones,or other systems that rely on friction and are limited in their torquecapacity. Additionally, these transmissions often involve relativelycomplicated control schemes so that torque and speed on input and outputare properly adjusted for different conditions.

Advantageously, the present disclosure provides a continuously variabletransmission that automatically changes speed and torque in response tovarying loads applied to the output shaft. Also, because thistransmission uses gears to transmit rotational force, rather than beltsor cones or other friction-based schemes, it experiences very smallpower losses, and is scalable to very high torque applications.

Shown in FIGS. 1 and 2 are side and perspective views of one embodimentof a continuously variable transmission 100 in accordance with thepresent disclosure. An exploded view is shown in FIG. 3, and a side,cross-sectional view is shown in FIG. 4. With reference to FIGS. 1-4, acontinuously variable transmission 100 in accordance with the presentdisclosure generally includes a first asymmetrical differential 102 anda second asymmetrical differential 104 that are linearly aligned along acommon transmission axis, indicated at 105, with a reduction gearassembly 106 disposed between them. The first asymmetrical differential102 is coupled to an input shaft or drive shaft 108 from a motor 110 orother mechanical device that provides a rotational driving force, andthe second asymmetrical differential 104 is coupled to an output shaft112, which transmits rotational force to some output device, such as adrive wheel (not shown) of a motor vehicle, for example.

The first asymmetrical differential 102 includes a first set of gears,including a high speed low torque bevel gear 116 a, a pair of opposingfirst differential bevel gears 118 a, and a low speed high torque bevelgear 120 a. The high speed low torque bevel gear 116 a and the low speedhigh torque bevel gear 120 a are both intermeshed with the firstdifferential bevel gears 118 a, but at opposite positions. The highspeed low torque bevel gear 116 a is fixedly attached to a proximal endof a high speed shaft 122, which is best seen in FIGS. 3-5. The lowspeed high torque bevel gear 120 a is fixedly attached to the sun gear124 of the reduction gear unit 106, as best seen in FIGS. 6-8. ViewingFIGS. 3 and 4, the first differential gears 118 a, are disposed ondifferential gear axle shafts 126 a, which are attached to a firstdifferential gear hub 128 a and a first armature 130 a of the firstdifferential 102.

Referring again to FIGS. 1, 3 and 4, the first armature 130 a includes ashaft extension 131 a that is fixedly attached to the input shaft 108,and is supported by an input shaft bearing 132. The proximal end of thehigh speed shaft 122 is not affixed to the input shaft 108, but isrotationally supported upon its own high speed shaft proximal bearing134 a, which is disposed within the first armature 130 a. The high speedshaft 122 can thus rotate at a speed that is independent of the speed ofrotation of the input shaft 108 and the first armature 130 a. The highspeed shaft 122 passes through openings in the differential gear hub 128a, the low speed high torque bevel gear 120 a, and the reduction gearunit 106, as described in more detail below with reference to FIGS. 3and 4. Its rotational speed is thus also independent of these otherstructures.

The second asymmetrical differential 104 is essentially a mirror imageof the first asymmetrical differential 102. As shown in FIGS. 1, 3 and4, the second differential 104 includes a second set of gears, whichinclude a second high speed low torque bevel gear 116 b, a pair ofsecond differential bevel gears 118 b, and a second low speed hightorque bevel gear 120 b. The second differential gears 118 b, aredisposed on differential gear axle shafts 126 b, which are attached to asecond differential gear hub 128 b and a second armature 130 b of thesecond differential 104. The high speed shaft 122 passes throughopenings in the second differential gear hub 128 b, the second low speedhigh torque bevel gear 120 b, and the reduction gear unit 106, as can bebest seen with reference to FIGS. 3 and 4.

The second high speed low torque bevel gear 116 b and the second lowspeed high torque bevel gear 120 b are both intermeshed with the seconddifferential bevel gears 118 b, but at opposite positions. The secondhigh speed low torque bevel gear 116 b is fixedly attached at a distalend of the high speed shaft 122, and thus rotates at the same speed asthe first high speed low torque bevel gear 116 a, as can be appreciatedby viewing FIGS. 3-5. The second low speed high torque bevel gear 120 bis fixedly attached to the carrier 140 of the reduction gear unit 106,as best seen in FIGS. 6-8 and 10-12.

Referring again to FIGS. 1, 3 and 4, the second armature 130 b includesa shaft extension 131 b that is fixedly attached to the output shaft112, and is supported by an output shaft bearing 136. The distal end ofthe high speed shaft 122 is not fixedly connected to the second armature130 b or to the output shaft 112, but is supported upon its own highspeed output shaft bearing 134 b, which is rotationally disposed withinthe second armature 130 b. As noted above, this configuration allows therotational speed of the high speed shaft 122 to be independent of thesecond armature 130 b and other structures of the continuously variabletransmission 100, including the reduction gear unit 106.

In FIGS. 1, 2 and 4 the bearings 132, 136 are shown supported on a base137, but this is for demonstration purposes only. In use, it isanticipated that the transmission 100 will be enclosed within a housing138, shown in dashed lines in FIG. 1. This housing 138 can enclose thefirst and second asymmetrical differentials 102, 104, the reduction gear106, and other components, as shown. The transmission housing 138 can besealed in the same way vehicle differential housings are commonlysealed, with a lubricant such as oil permanently disposed inside, asindicated by the fluid surface 139, shown in FIG. 1.

As used herein, the term “asymmetrical differential” has reference to agear differential in which a single rotational input (e.g. input shaftor drive shaft) enters one side of the device, and two coaxial outputshafts (one smaller shaft disposed inside a larger hollow shaft) exit ona different, common side. Shown in FIG. 5A is a perspective view of anasymmetrical differential 102 like this, and FIG. 5B provides anexploded perspective view of the same device. The asymmetricaldifferential 102 is similar in function to gear differentials that arecommonly used in automobiles and other machines to transmit torque froma drive shaft to a pair of drive wheels, but is different inarrangement. Shown in FIG. 6A is a side view of a conventionallimited-slip differential 200, and FIG. 6B provides a cross-sectionalview of the same. In this type of common differential, a drive shaft 208enters a first side of the differential 200, and a pair of drive axles214 a, 214 b exit on opposing lateral sides (e.g. left and right) of theunit, extending to respective drive wheels (not shown). A pinion gear210 is attached to the drive shaft 208, and drives a crown wheel 212,which rotates about an axis that is aligned with the axis of the driveaxles 214, and perpendicular to the axis of the drive shaft 208.

Within the differential 200, a pair of differential bevel gears 218 areattached to a rotating armature 230. The armature 230 is fixedlyattached to the crown wheel 212, and rotates with it. The differentialbevel gears 218 are intermeshed with drive gears 216 and 220, which areconnected to the respective axles 214 a, b. The axles, however, are notconnected to the crown wheel 212 or the armature 230. Consequently, thedifferential bevel gears 218 transmit torque from the drive shaft 208 tothe drive axles 214, and can allow a different degree of torque andspeed to flow to the respective axles 214 if one of them encounters moreresistance than the other. For example, when an automobile traverses asharply curved path, a drive wheel that is on the inside of the curvefollows a shorter path, while the outer drive wheel experiences a longerpath. If both drive wheels were driven with the same torque and speed,one of them would tend to slip. With the differential 200 of FIGS. 6A,6B, on the other hand, the axles 214 a, b can rotate at different rates.If one of the axles 214 experiences more resistance to motion, thatresistance with be mechanically transmitted into the differential 200through the respective drive gear 216, 220. Specifically, where therotational speed of the armature 230 does not change, rotationalresistance by one of the drive gears 216, 220 will cause thedifferential bevel gears 218 to rotate faster and thus transmit a higherspeed of rotation to the opposite drive gear. The differential 200 thusprovides two outputs (axles 214 a, b) that can have different rotationalspeeds, depending on the resistance that each experiences. In thedifferential of FIGS. 6A, B, if one axle 214 were completely stopped,and prevented from rotation, all torque from the drive shaft 208 wouldbe transmitted to the other axle 214.

The asymmetrical differential 102 disclosed herein likewise provides twooutputs that can have different rotational torque and speed, dependingon the resistance that each experiences, but these output shafts exitthe device on the same side, and are aligned with the input shaft. Shownin FIG. 7 is. With reference to FIGS. 3-5 and FIGS. 7A and 7B, whichshow close-up side and cross-sectional views of an asymmetricaldifferential as disclosed herein, it can be seen that the input shaft108 is fixedly connected to the shaft extension 131 a, which is fixedlyconnected to the armature 130 a. Attached to the armature 130 a bybearing shafts 126 a are a first pair of differential bevel gears 118 a,which intermesh with the high speed low torque bevel gear 116 a and thelow speed high torque bevel gear 120 a. The high speed low torque bevelgear 116 a is fixedly connected to the high speed shaft 122, whichpasses through the hub 128 a and through the low speed high torque bevelgear 120 a. The low speed high torque bevel gear 120 a is fixedlyattached to a hollow shaft output structure, which in this embodiment isthe planet gear 124 for the reduction gear unit 106. The high speedshaft 122 thus extends through the hollow of the planet gear 124. Therotational input via the input shaft 108 is thus transmitted to twocoaxial output shafts 122, 124, which are all aligned along thetransmission axis 105.

Thus, instead of drive axles or shafts exiting the differential on theleft and the right to opposing axles, as in FIGS. 6A, B, both drivenaxles 122 and 141 exit the differential 102 on same side. The high speedcenter shaft 122 rotates with the high speed bevel gear 116 a, and isthe functional equivalent of a first one of the drive gears (e.g. 218)in FIGS. 6A, 6B, while the low speed high torque shaft extension 141 isthe functional equivalent of the second one of the drive gears (e.g.220) in FIGS. 6A, 6B. This is possible because the high torque shatextension 141 is a hollow tube that the low torque shaft 122 passesthrough. Thus, both output axles 122, 141 extend toward a single side,where they are connected to the corresponding shafts of the seconddifferential 104 and the reduction gear 106, respectively.

Advantageously, the second differential 104 is also an asymmetricaldifferential, and is configured as a mirror image of the firstasymmetrical differential. By using two asymmetrical differentials, theforce of the motor (110 in FIG. 1) is divided into two different outputsby the first asymmetrical differential 102, each output having anindependent torque and speed. One of these outputs (the high torqueextension 141) is attached to the reducing gearbox 106, then recombinedwith the other output (the high speed shaft 122) via the secondasymmetrical differential 104. The result is a single output shaft 112that automatically and naturally responds to changes in loads applied toit, because of the reduction gear 106, as described more fully below.

The reduction gear unit 106, which is disposed between the firstdifferential 102 and the second differential 104, is best shown in FIGS.3 and 10-12. It is to be understood that, while the reduction gear 106unit shown and described herein is a planetary reduction gear, othertypes of reduction gear systems can also be used. For example, it isbelieved that a non-planetary compound gear system or a worm drivereduction gear could also arranged to be used in this application. Itwill also be appreciated that the gear ratio of the reduction gear unit106 can vary. In one embodiment, an approximate gear ratio of 3:1 hasbeen used. However those of skill in the art will appreciate that thistype of continuously variable transmission can be constructed with othergear ratios. Any gear ratio can be selected and embodied in a singlereduction gear unit 106, though the size of the reduction gear unit 106will be affected by this choice. A higher gear ratio can be used inapplications where a greater range of torque loads are anticipated. Forexample, where this transmission is used with vehicles that are designedfor off-road use or to carry heavy loads, such as trucks and the like,the transmission 100 can have a reduction gear unit 106 with a highergear ratio (e.g. 10:1). The maximum gear ratio (and lowest speed) willnaturally engage only when the highest torque demands are applied. Whenthe load is lighter, a lower gear ratio will naturally operate, thusallowing higher speeds if desired.

It is also to be appreciated that multiple reduction gear units 106 canbe attached in series between the first differential 102 and the seconddifferential 104, to provide a very high gear ratio, if desired. Wheremultiple reduction gear units are attached in series—i.e. the outputshafts of adjacent reduction gear units are attached to the input shaft(i.e. sun gear) of the next reduction gear—the gear ratio can bemultiplied. For example, two 3:1 reduction gear units attached in serieswill provide a gear reduction of 9:1. Accordingly, three reduction gearunits connected in series, each having a reduction ratio of 10:1, willprovide an overall gear reduction of 1,000:1, for example. It is to beunderstood that these possible gear ratios and configurations are merelyexamples. A reduction gear unit or group of reduction gear units can beconfigured to provide any desired gear ratio.

It is also to be appreciated that the orientation of the reduction gearcan be reversed, so that instead of a ratio of 3:1, for example, theratio becomes 1:3, and the term “reduction gear,” as used herein, isintended to refer to a device that provides a gear ratio in eitherdirection, whether upward or downward relative to the input shaft. Agear ratio in this direction may be desirable for coupling of thetransmission 100 to an internal combustion engine, for example, in whichthe normal operating speed of the engine is relatively high compared tothe desired speed of the output shaft. Again, multiple sequentialreduction gear units having this sort of orientation can be used toprovide a very high gear ratio. Using the example given above, wherethree reduction gear units are connected in series, each having areduction ratio of 1:10, this will provide an overall gear reduction of1:1,000.

Viewing FIGS. 10-12, the reduction gear unit 106 generally includes asun gear 124, a group of planet gears 142, a planet gear carrier 140,and a ring gear 146 that is fixed in position. In the embodiment of FIG.12, the carrier 140 includes two portions that are generally disk-shapedand are parallel to each other. The planet gears 142 (and the ring gear146) are sandwiched between the two portions of the carrier, and theplanet gears 142 are supported upon planet gear bearings 148 that aresupported by the two portions of the carrier. The second low speed hightorque bevel gear 120 b extends from and is fixedly attached to thesecond portion of the carrier 140. In the embodiment of FIGS. 10 and 11,however, the carrier 140 is a single piece that lies on one side of thering gear 146, and the second low speed high torque bevel gear 120 b isattached to this one piece.

The planet gears 142 are intermeshed with the sun gear 124 in the centerof the reduction gear unit 106, and are intermeshed with the teeth 152around the perimeter of the fixed ring gear 146. As is well known, a sunand planet gear system can provide a gear reduction between an inputshaft and an output shaft, depending on the gear ratios of the sun andplanet gears 124, 142 and the ring gear 146. The ratios of these gearscauses the carrier 140 (and thus the second high torque gear 120 b) torotate at a speed that is different than the speed of the first hightorque gear 120 a.

The first low speed high torque bevel gear 102 a and the sun gear 124are connected by the extension 141, and can be an integral unit. A gearadjustment wheel 144, having gear teeth 150, can also extend from theextension 141, and can be used for adjusting the degree to which thereduction gear 106 operates, as discussed below. As shown in FIG. 4, thebevel gear 102 a, sun gear 124 and extension 141 can be rotationallysupported upon the high speed shaft 122 by bearing units 154, 156, andthe carrier 140 can be rotationally supported upon the shaft extension141 by a carrier bearing 158. With this configuration, the unitincluding the first high torque bevel gear 102 a, the sun gear 124 andthe extension 141 can freely rotate at a different speed than thecarrier 140.

Operation of this continuously variable transmission is as follows. Whenthe motor 110 is activated, turning the input shaft 108 in a givendirection, this will drive the output shaft 112 in the same direction.The motor 110 is connected to the first asymmetrical differential 102,which divides the torque of the input shaft 108 into two parts. Thefirst differential armature 130 a is directly attached to the inputshaft 108, and is thus driven by the motor 110. Since the firstdifferential bevel gears 118 a are rotationally mounted upon the firstarmature 130 a with axles 126 a and center hubs 128 a, the rotationalaxes of these bevel gears 118 a rotate with the armature. As thisarrangement rotates, the first differential bevel gears 118 a will makecontact with and drive the high speed/low torque shaft 122 by makingcontact with the first high speed low torque gear 116 a. At the sametime, the first differential bevel gears 118 a will also make contactwith and drive the first low speed/high torque gear 120 a, which isconnected to drive the sun gear 124 of the reduction gear unit 106.

The intermeshing of the gears 118 a with the gears 116 a and 120 a(which are free to rotate independently of the input shaft 108), willnaturally distribute the rotational energy of the armature 130 a intothe gears 116 a and 120 a. Since the high speed input gear 116 a and lowspeed input gear 120 a rotate independently of each other, the firstasymmetrical differential 102 thus divides the torque of the input shaftinto two output streams—the high speed shaft 122 and the high torqueshaft extension 141.

At this point both the high speed/low torque shaft 122 and the lowspeed/high torque input gear 120 a are driven with equal force. At thispoint, however, a basic principle of mechanics comes into play. Inmechanical systems, where a force is divided between two output streams,the mechanical force will naturally follow the path of least resistance.Because the low speed/high toque input gear 120 a is attached to theplanetary reduction gear unit 106, which has inherently more resistancedue to its gearing, the motor force is naturally biased toward the pathof least mechanical resistance, which is the freely spinning highspeed/low torque shaft 122. Where the output shaft 112 has no rotationalresistance upon it, the very existence of the reduction gear 106 willnaturally cause most or all of the torque from the input shaft 108 toflow through the high speed shaft 122 simply because fewer mechanicalelements are connected to that shaft. Every element that rotates in thetransmission 100 introduces a certain level of resistance simply frominertia and friction. Transmission of rotation through the reductiongear 106 to the output shaft 112 involves the rotation of several moremechanical elements (the sun gear 124, the planet gears 142, the carrier140), in addition to the different gear ratio, than does transmission ofrotation to the output shaft 112 through the high speed shaft 122.Consequently, the inertia of the reduction gear 106 will cause it toremain still when there is no resistance upon the output shaft 112.

In the low resistance situation, the rotational force of the motor 110thus drives the high speed/low torque shaft 122 and its fixed high speedlow torque gears 116 a, 116 b. The second high speed low torque gear 116b in turn drives the second differential bevel gears 118 b, which inturn rotates the armature 130 b of the second differential 104, and thusrotates the output shaft 112. With the transmission configuration shownherein, where no resistive load is applied to the output shaft 112, theoutput shaft will be allowed to run freely, with essentially the samespeed as the input shaft 108, but with relatively low torque-i.e. thetorque provided by the motor 110 at its running speed, which may itselfbe geared down prior to entering the transmission 100. In thiscondition, the output shaft 112 will turn at the same speed (i.e. aneffective gear ratio of 1:1) and direction as the high speed/low torqueshaft 122 and the high speed low torque gears 116 a, b. As long as thereis little or no resistive force to the output shaft 112, the lowspeed/high torque gear 120 a will not rotate.

However, as a resistive load is applied to the output shaft 112, thetorque and speeds of the components of the transmission 100 will beginto migrate. With a resistive load applied to the output shaft 112, thisimposes greater resistance upon the high speed/low torque shaft 122 andthe high speed bevel gear 116 a. When the mechanical resistance of thisgear 116 a comes to equal or exceed that of the reduction gear 106, thefirst high speed gear 116 a will begin to slow down, and the lowspeed/high torque gear 120 a will begin to rotate. In this way,rotational force will begin to be transmitted to the first high torquebevel gear 120 a, thus turning the reduction gear 106.

Because rotation of the low speed/high torque gear 120 a feeds into theplanetary reduction gearbox 106, which produces a lower speed, highertorque output, a portion of the rotational force of the input shaft 108is transmitted through the reduction gear and the second high torquegear 120 b, thus providing greater torque (by virtue of the gear ratioof reduction gear unit 106) at a lower speed for driving the outputdifferential 104, and thus the attached output shaft 112, to overcomethe load. As the load upon the output shaft 112 continues to increase,the speed will continue to decrease, and the portion of the load borneby the low speed/high torque gear 120 b will increase to bear the load,but at a lower speed. Throughout this entire process, it is presumedthat the rotational speed of the input shaft 108 remains constant.

The result of this operation is a natural “balancing” or “blending” oftorque and rotational speed in order to bear the increased resistiveforce applied to the output shaft 112. With a constant power input, asthe resistive force to the output shaft 112 increases, the output speedwill naturally tend to drop, but the output torque will increase. On theother hand, if the load is decreased, with no change in input power, theopposite happens—the output shaft 112 will rotate faster with lesstorque, as expected. By varying the resistance to the output shaft 112,the continuously variable transmission 100 “balances” or “blends” thecombination of speed and torque to match the load applied.

It is notable that the motor 110 does not necessarily change speed orexperience a change of output power as this torque/speed balancing orblending occurs. These factors can be held constant, if desired. On theother hand, the speed and power of the motor 110 can be changed at willto obtain a desired output speed for a given torque load. Thus, aconstant motor output can be maintained while the torque output andspeed are allowed to vary with changes in load, or a constant outputspeed can be maintained by modifying the motor input power and speed astorque loads change. This can allow motors to be operated in a desiredspeed and output torque range for maximum efficiency.

Control of this continuously variable transmission 100 can be relativelysimple. Shown in FIG. 13 is a partial schematic side view of thecontinuously variable transmission of FIG. 1, showing an embodiment ofan electronic control system for use with this transmission connected toan electric motor 110 that is powered by a battery 190. The controlsystem generally includes a motor controller 180, a CPU 182, and a speedsensor 186 that is connected to the output shaft 112. The CPU receivesinput from the speed sensor 186 indicating the rotational speed of theoutput shaft 112, and also receives input from a speed demand system188, which can include user input devices like a throttle pedal, acruise control system or a control switch or speed selector device ofsome sort. The CPU 182 provides commands to the motor controller 180,which selectively controls the power from the battery 190 to the motor110. This adjusts the rotational speed of the input shaft, which ismodulated through the transmission 100 in the manner discussed above.Specifically, the first and second asymmetrical differentials 102, 104and the reduction gear 106 naturally balance the input power to providea desired speed of the output shaft 112 for given operating conditions.When conditions change, the motor control settings at any given timewill naturally cause the transmission to rebalance, thus changing thespeed of the output shaft 112, and causing the CPU 182 to readjust themotor parameters to compensate.

As shown in FIG. 13, the transmission 100 can also include a clutch 184,such as a power-operated clutch, coupled to the input shaft, so that theinput shaft 108 can be selectively engaged with the transmission 100. Insystems that use an electric motor, as shown in FIG. 13, it may bepossible and even desirable to omit the clutch 184. This is possiblebecause with an electric motor, stopping the system can simply be amatter of stopping power to the motor 110. However, in some othersystems, such as a vehicle powered by an internal combustion engine, theengine normally idles when the vehicle is stopped. Thus, it is desirableto disconnect the engine shaft from the transmission until is it desiredto resume transmitting force through the transmission.

The clutch 184 can also be provided to prevent back drive—that is,reverse rotation being transmitted through the transmission 100 into theinput shaft 108. It is to be appreciated that the continuously variabletransmission 100 can operate in either rotational direction. If theoutput shaft 112 is completely stalled or resisted, and the input motor110 is still driving the input shaft 108 (a condition under which aninternal combustion engine would stall and die), the gears of thetransmission 100 create a back drive situation, wherein the high speedshaft 122 is driven in a reverse direction. In some applications, a backdrive situation can be desirable as an automatic safety feature. Inother applications, however, it may be undesirable. Advantageously, theclutch 184 allows disengagement of the transmission 100 from the inputshaft 108 to prevent this. This can be done in a configuration in whichthe clutch 184 is a power-operated clutch, controlled by the CPU 182based on input from the speed sensor 186. Alternatively, the clutch 184can be a purely mechanical overrunning clutch, which only allowstransmission of rotation in one direction, and thus automaticallyprevents reverse operation.

As another alternative, back drive can be prevented by providing aclutch elsewhere in the transmission 100. For example, viewing FIGS. 3,4 and 5A-5B, bearing 134 a can be a roller bearing clutch.Advantageously, a one way roller bearing clutch 134 a disposed at theproximal end of the high speed shaft 122 can prevent back drive, thuseliminating this potential issue where it could present problems.

While reverse operation may or may not be desirable, the transmission100 can still transmit torque either from the input shaft 108 to theoutput shaft 112, or from the output shaft 112 to the input shaft,whether this is done with single direction operation, or bi-directionaloperation. For example, where the transmission 100 is powered androtating in its drive direction, and power to the motor 110 is cut,continued rotation of the output shaft 112 (e.g. due to inertia) willtend to transmit torque through the transmission 100 to the output shaft108, with the asymmetrical differentials 102, 104 and reduction gear 106naturally balancing the transmission of torque just as it does in normaloperation. This feature can be useful in electric vehicles, for example,providing a dynamic braking system that allows the generation ofelectricity from the inertia of the vehicle, while slowing the vehicle.In a vehicle with an internal combustion engine, this mode of operationcan provide the effect of engine braking, which can be useful for largetrucks and smaller vehicles descending steep hills.

Advantageously, since this continuously variable transmission 100 usesgears for transmitting torque, rather than friction-based structuresthat are commonly used in many continuously variable transmissions, ithas relatively low mechanical losses, and it is scalable for use withboth large and small machines, from small motorized toys to industrialrobots, motor vehicles and heavy equipment with high torque motors.Additionally, the simplicity of this transmission makes it economical,durable, and easy to maintain. Since this transmission does not includeshifting gear trains, it is considered likely to have a very long lifewith very little need for maintenance.

An additional feature of the continuously variable transmission shownherein is illustrated with reference to FIGS. 14-15 and 16-17. Sincethis transmission naturally balances torque and output speed based onits own internal resistance, a simple mechanism can be added to allowselective balancing of these forces. Shown in FIG. 14 is a perspectiveview of an embodiment of a continuously variable transmission 100 inaccordance with the present disclosure, having a gear range selectordevice 300. As discussed herein, this transmission includes an outputshaft 112, and an input shaft 108, which is attached to a motor 110 thatprovides power to the transmission. The transmission 100 includes firstand second differentials 102, 104, with a reduction gear 106 disposedbetween them.

As noted above, the first asymmetrical differential 102 includes a gearadjustment wheel 144, having gear teeth 150, which extends from theextension (141 in FIGS. 4, 5A-5B, 7A-7B) that is connected to the firsthigh torque gear 120 a. The teeth 150 of the gear adjustment wheel 144are intermeshed with a braking gear 302 of a gear range selector device300. An exploded perspective view of the gear range selector device 300is shown in FIG. 15. The gear range selector device 300 is amodification of a reciprocating oil gear pump. The device 300 includes apair of pump gears 310 that are tightly enmeshed and rotate together tocirculate a fluid (e.g. oil) within a housing 308. The trapped fluid isrecirculated through a channel that passes by an adjuster 304. The firstof the two pump gears 310 is mounted on an axle 312 that extends throughthe housing cover 316 and is affixed to the braking gear 302.

Manipulation of the adjuster 304 can vary a resistance to the flow ofthe fluid within the housing 308, and thereby resist rotation of thebraking gear 302. The same principal of fluid dampening is used inadjustable oil shocks. One advantage of this gear range selector device300 is that it does not impose wear on friction plates or the like inorder to produce a speed reduction. The adjuster 304 allows variation inthe degree of resistance applied to flow of the fluid, and thus allowsvariation in the degree of braking applied by the gear range selectordevice 300. While the adjuster 304 is shown configured as a knob formanual twisting, it is to be appreciated that other devices can be used,such as a servo motor under the control of a computer controller (e.g.CPU 182 in FIG. 13).

In operation, the gear teeth 306 of the braking gear 302 are engagedwith the teeth 150 of the gear adjustment wheel 144. With no resistanceapplied to the braking gear 302, the transmission will operate in theordinary load balancing mode, as discussed above. However, when theadjuster 304 is rotated to apply resistance to the adjustment gears 310,this applies a braking force from the braking gear 302 to the gearadjustment wheel 144, and thus to the input of the reduction gear unit106. This additional resistance applied to the reduction gear 106naturally reduces the relative proportion of torque distributed throughthe reduction gear 106, and thus naturally distributes more torquethrough the high speed shaft 122, in the manner discussed above.Accordingly, with some level of resistance applied by the gear rangeselector 300, the transmission will provide a higher speed at the outputshaft 112, but with lower torque. If the gear range selector device 300is adjusted to completely stop rotation of the gear adjustment wheel144, this will completely stop the reduction gear 106, and will thusdistribute all rotation through the high speed shaft 122.

The gear range selector device 300 thus allows adjustment of the degreeto which the reduction gear 106 operates. No resistance from the gearrange selector 300 allows standard operation, with resistance on theoutput shaft 112 naturally causing the transmission to gear down forgreater torque, but at a reduced speed (unless the output of the motor110 is adjusted). This can be desirable for bearing heavy loads whilemaintaining a desired level of efficiency, and without adjusting theoperational parameters of the motor 110. On the other hand, higherresistance on the gear range selector 300 allows the transmission toprovide higher speed, though the torque on the output shaft 112 will belimited to the torque provided by the input shaft 108. This can bedesirable for conditions where high speed is desired and loads aresmall, or where high speed is desired and any additional torque that isneeded is provided by adjusting the operational parameters of the motor110.

It is to be appreciated that application of braking force on the gearadjustment wheel 144 does not impose significant mechanical losses (e.g.parasitic losses) upon the transmission because it is not providing anoverall braking force upon the transmission 100. Instead, a brakingforce upon the gear adjustment wheel 144 merely redistributes rotationalmotion to other parts of the transmission 100 (e.g. to the high speedshaft 122), which are always free to rotate. Thus, there is little or noparasitic loss from use of the gear range selector device 300.

Another embodiment of a continuously variable transmission 100 having agear range selector device 400 is shown in FIG. 16, and an explodedperspective view of the gear range selector device 400 is shown in FIG.17. Again, the transmission 100 includes an output shaft 112, and aninput shaft 108 that is attached to a motor 110, with first and seconddifferentials 102, 104, and a reduction gear 106 disposed between them.In this embodiment, the teeth 150 of the gear adjustment wheel 144 areintermeshed with a braking gear 402 of a gear range selector device 400,which, as shown in FIG. 17. The gear range selector device 400 includesa base 408, the braking wheel 402 with gear teeth 406, a brake ring 410,and an adjuster 404. The adjuster 404 is shown configured as a knob formanual twisting, but it is to be appreciated that other adjuster devicescan be used, such as a servo motor under the control of a computercontroller (e.g. CPU 482 in FIG. 18).

In operation, the gear teeth 406 of the braking gear 402 are engagedwith the teeth 150 of the gear adjustment wheel 144. With no resistanceapplied to the braking gear 402, the transmission will operate in theordinary load-balancing mode discussed above. However, when the adjuster404 is rotated to apply resistance to the braking gear 402 via the brakering 410, this applied resistance to the gear adjustment wheel 144, andthus redistributes torque between the reduction gear 106 and the highspeed shaft 122, in the manner discussed above.

A configuration of a computerized control system for a transmission 100having a gear range selector device 400 is illustrated in the partialschematic perspective view of FIG. 18. This control system is similar tothat of FIG. 13. In FIG. 18 the transmission 100 is connected to anelectric motor 110 that is powered by a battery 490. The control systemgenerally includes a motor controller 480, a CPU 482, and a speed sensor486 that is connected to the output shaft 112. The CPU 482 receivesinput from the speed sensor 486 indicating the rotational speed of theoutput shaft 112, and also receives input from a speed demand system488, which can include user input devices like a throttle pedal, acruise control system or a control switch or speed selector device ofsome sort. The CPU 482 provides commands to the motor controller 480,which selectively controls the power from the battery 490 to the motor110. This adjusts the rotational speed of the input shaft 108, which ismodulated through the transmission 100 in the manner discussed above.Though not shown in FIG. 18, a clutch can also be provided on the inputshaft 108 and controlled via the CPU 482.

As discussed above, when operating conditions change, settings of themotor controller 480 can change under command of the CPU 482 at anygiven time in order to cause the transmission 100 to rebalance, thuschanging the speed and/or power of the output shaft 112. Advantageously,this control system also includes a servo motor 492, which is coupled tothe adjuster 404 of the gear range selector 400. Thus, when a signal isreceived by the CPU 482 indicating a need to increase the speed of theoutput shaft 112 without increasing (or increasing only to some limiteddegree) the speed of the input shaft 108, the CPU can send a signal tothe servo motor 492, causing it to impose some degree of resistance tothe gear adjustment wheel 144, as needed. The gear range selector device400, as controlled by the CPU 482 and subject to input from a userthrough the speed demand device 488 and the speed and torque sensor 486,thus allows adjustment of the degree to which the reduction gear 106operates, allowing the gear ratio of the transmission 100 to be selectedif desired.

The present disclosure thus provides a continuously variabletransmission that passively senses and balances loads, allowing highefficiency. It automatically balances output speed and torque dependingon its input and the load upon the output shaft, and does so smoothlyand imperceptibly, without abrupt shifting between different gear setsand without the need for a transmission that is heavy, highlycomplicated, and subject to significant maintenance and wear. Its modeof operation can also be selectable, so that a user can obtain a desiredspeed by adjusting the load-balancing characteristics of thetransmission.

The continuously variable transmission disclosed herein can be used in awide variety of applications, such as automobiles and other vehicles, incranes, winches and hoists, heavy equipment, robots and otherapplications. This transmission can be used in some current applicationsto take the place of multiple motors. For example, in some applications,such as robotics, different lifting and moving conditions are common.For example, a single robot may be configured to move large loads, andalso to move without any load. The designer of such a robot may be facedwith providing one vary large motor for both applications, in which casethe robot may move very slowly and inefficiently when under no load, orproviding two motors for the different conditions, which is more costlyfor producing the machine. With the present transmission system, incontrast, a single motor can move a mechanical device quickly when noload is applied, and automatically slow its speed to bear a heavy loadwhen required. The size of the motor can thus be optimized, and the useof multiple motors reduced.

Although various embodiments have been shown and described, the presentdisclosure is not so limited and will be understood to include all suchmodifications and variations are would be apparent to one skilled in theart.

What is claimed is:
 1. A continuously variable transmission, comprising:a first asymmetrical differential, having a transmission input shaft anda first output shaft, aligned along a transmission axis; a secondasymmetrical differential, having a transmission output shaft and afirst input shaft, aligned along the transmission axis; and a reductiongear unit, coupled between the first output shaft of the firstasymmetrical differential and the first input shaft of the secondasymmetrical differential, rotation of the input shaft at a first inputspeed and torque being converted into rotation of the transmissionoutput shaft at a second output speed and torque that variesindependently of the first input speed and torque in response to arotational resistance on the transmission output shaft.
 2. Thecontinuously variable transmission of claim 1, wherein the reductiongear unit has a gear ratio in the range of 1,000:1 to 1:1,000.
 3. Thecontinuously variable transmission of claim 1, wherein the reductiongear further comprises: a sun gear, fixedly coupled to the first outputshaft; a fixed ring gear, encircling the sun gear; a plurality of planetgears, coupled between the sun gear and the ring gear; and a carrier,fixedly coupled to the first input shaft, supporting a bearing shaft foreach of the planet gears.
 4. The continuously variable transmission ofclaim 1, further comprising a clutch, disposed upon the transmissioninput shaft, configured to allow selective engagement of thetransmission input shaft with a drive shaft.
 5. The continuouslyvariable transmission of claim 1, further comprising an overrunningclutch, disposed upon the input shaft, configured to allow rotation ofthe input shaft in one direction only.
 6. The continuously variabletransmission of claim 1, further comprising: a speed sensor, coupled tothe output shaft; and a controller, coupled to receive input from thespeed sensor and from a user, and to provide control output suitable fora motor that can be coupled to the input shaft, based on the motorcontrol inputs and the speed of the output shaft.
 7. The continuouslyvariable transmission of claim 6, further comprising a gear rangeselector, operatively coupled to the controller and engaged with thereduction gear, configured to selectively inhibit rotation of thereduction gear in response to signals from the controller, and therebymodify the rotational speed and torque of the output shaft.
 8. Thecontinuously variable transmission of claim 1, further comprising a gearrange selector, engaged with the reduction gear and configured toselectively inhibit rotation of the reduction gear and thereby modifythe rotational speed and torque of the output shaft.
 9. The continuouslyvariable transmission of claim 1, further comprising: an independentlyrotatable high speed shaft, extending through the reduction gear fromthe first asymmetrical differential to the second asymmetricaldifferential and coaxially passing through the first output shaft andthe first input shaft; a first low torque bevel gear, disposed at afirst end of the high speed shaft and comprising a part of the firstasymmetrical differential; and a second low torque bevel gear, disposedat a second end of the high speed shaft and comprising a part of thesecond asymmetrical differential, a degree of torque transmitted via thehigh speed shaft through the transmission to the output shaft beinginversely proportional to a magnitude of rotation of the reduction gear.10. The continuously variable transmission of claim 1, furthercomprising a one-way clutch, coupled to the high speed shaft, configuredto prevent transmission of reverse rotation from the high speed shaft tothe input shaft.
 11. The continuously variable transmission of claim 1,further comprising a housing, surrounding and containing the first andsecond asymmetrical differentials and the reduction gear.
 12. Acontinuously variable transmission, comprising: a first asymmetricaldifferential, having an input shaft configured for connection to anoutput shaft of a motor, and a coaxial pair of first output shafts,including an outer output shaft and an inner output shaft, the inputshaft and the output shafts being disposed along a common transmissionaxis; a second asymmetrical differential, having an output shaft, and acoaxial pair of input shafts, including an outer input shaft and aninner input shaft, the output shaft and the input shafts being disposedalong the transmission axis, and the inner input shaft being anextension of the inner output shaft; and a reduction gear unit, having agear ratio, disposed between the first and second asymmetricaldifferentials, having a reduction gear input coupled to the outer outputshaft, and a reduction gear output coupled to the outer input shaft,whereby rotation of the input shaft of the first asymmetricaldifferential at a first input speed and torque is converted intorotation of the output shaft at a second output speed and torque thatvaries independently of the first input speed and torque in directresponse to rotational resistance on the output shaft.
 13. Thecontinuously variable transmission of claim 12, further comprising aclutch, configured to allow at least one of (i) selective engagement ofthe input shaft of the continuously variable transmission with the driveshaft and (ii) rotation of the input shaft in one direction only,independent of a rotational direction of the output shaft.
 14. Thecontinuously variable transmission of claim 11, further comprising: aspeed sensor, coupled to the output shaft; and a controller, coupled toreceive input from the speed sensor and from a user, and to providecontrol output suitable for a motor that can be coupled to the inputshaft, based on the motor control inputs and the speed of the outputshaft.
 15. The continuously variable transmission of claim 12, furthercomprising a gear range selector, operatively coupled to the controllerand engaged with the reduction gear, configured to selectively inhibitrotation of the reduction gear in response to signals from thecontroller, and thereby modify the rotational speed and torque of theoutput shaft.
 16. A continuously variable drive system, comprising: amotor, having a drive shaft; a transmission output shaft, disposed alonga transmission axis; a first asymmetrical differential, having, alongthe transmission axis, an input shaft coupled to the drive shaft, andfirst and second coaxial output shafts; a reduction gear, having aninput coupled to the first output shaft of the first asymmetricaldifferential, and an output; and a second asymmetrical differential,having, along the transmission axis, a first input shaft coupled to theoutput of the reduction gear, and second input shaft coupled to thesecond output shaft of the first asymmetrical differential, a speed andtorque of the transmission output shaft varying independently of a speedand torque of the drive shaft in direct response to rotationalresistance on the transmission output shaft.
 17. The continuouslyvariable drive system of claim 16, further comprising a clutch, coupledbetween the drive shaft and the input shaft of the first asymmetricaldifferential.
 18. The continuously variable drive system of claim 16,further comprising a speed sensor, coupled to detect a speed of theoutput shaft; an operator input device, configured to receive motorcontrol inputs from a user; and a controller, coupled to receive inputfrom the speed sensor and from the operator input device, and to providecontrol output to the motor, based on the motor control inputs and thespeed of the output shaft.
 19. The continuously variable drive system ofclaim 18, further comprising a gear range selector, operatively coupledto the controller and engaged with the reduction gear, configured toselectively inhibit rotation of the reduction gear in response tosignals from the controller, and thereby modify the rotational speed andtorque of the output shaft.
 20. The continuously variable drive systemof claim 16, wherein the reduction gear comprises a planetary reductiongear system.